Exploring the Evolutionary History of Humans: From Rodents to Primates

[SW VandeCarr]

I'm wondering if someone can help me. I'm trying to find material on our pre-primate ancestors. From informal discussions I've heard that our line goes back through rodents, small lizards or a salamander type of reptile, through some long extinct amphibian and fish back to eels and sea worms of some kind. I know our full ancestral line has not been worked out, but I thought there might be some informed theories about this. It seems we are not descended from the most prestigious of lines.

 

[Ophiolite]

We are alive today after 3.8 billion years of evolution. We are members of a line that employed endosymbiosis to become eukaryotes, introduced sexual reproduction, developed multicellularity and tissue specialisation, left the sea provisionally, then permanently, and along the way survived at least five mass extinctions.

Could you tell me what is not prestigious about that?

I suggest you buy, read and study The Ancestor's Tale by Richard Dawkins. It will provide all the answers you are currently seeking.

 

[SW VandeCarr]

Could you tell me what is not prestigious about that?

My question was about our specific ancestral line. "Prestige" is a judgmental, non-scientific word in this context. I was simply pointing out that our ancestors were not the dominant species of past eras. But the history dominant species is that they don't survive. We are the dominant species on the Earth today. I have several books by Dawkins and Gould (but not the one you suggested) as well as a very detailed "Tree of Life" graph but they don't clearly answer my specific question: Are we descended from rodents, small lizards, eels and sea worms? If so, we should be respectful of these creatures; especially rodents.

 

[mgb_phys]

There is a fantastic book on that topic , The Ancestor's Tale by richard Dawkins
http://en.wikipedia.org/wiki/The_Ancestor's_Tale

edit Ophiolite already recommended it.

 

[SW VandeCarr]

There is a fantastic book on that topic , The Ancestor's Tale by richard Dawkins
http://en.wikipedia.org/wiki/The_Ancestor's_Tale

edit Ophiolite already recommended it.

Found it. Thanks. Like I said, we should look more kindly on rats and mice. (I'm not in a convenient location to shop for scientific books right now, but I will look for this book when I can.

EDIT: I specifically wanted to know how much knowledge we have regarding a description of the species at the 'rendezvous points' along the direct human line. For example, at the rendezvous point of the human line with rodents, did that species more closely resemble a mouse or shrew or something else? How much information (or theoretical descriptions) do we have on these branch point species along the human line? I'd be happy to find educated "best guess" descriptions of these ancestors.

 

[Ophiolite]

"Prestige" is a judgmental, non-scientific word in this context.

Precisely. So I did not understand why you would use it.

But the history dominant species is that they don't survive.

The history of all species is that they do not survive. Dominance has very little to do with it.

I was simply pointing out that our ancestors were not the dominant species of past eras... We are the dominant species on the Earth today.

In what sense? Capable of destroying more species than any other? The only ones with ipods? How do you define dominant. Are you sure it is not another judgmental, non-scientific word?

Are we descended from rodents, small lizards, eels and sea worms? If so, we should be respectful of these creatures; especially rodents.

So it is quite acceptable to be disrespectful of creatures we are not descended from? I'll keep that in mind.

I do have some good news for you. None of the rodent species alive today represent in any way the rodents from whom we evolved. So it's perfectly alright to swear at rats, fart in front of mice, and steal food from guinea pigs.

 

[SW VandeCarr]

Precisely. So I did not understand why you would use it. The history of all species is that they do not survive. Dominance has very little to do with it. In what sense? Capable of destroying more species than any other? The only ones with ipods? How do you define dominant. Are you sure it is not another judgmental, non-scientific word?

Are you going to deny the common perceptions? I never indicated I supported such perceptions. The common perception is that our species has a some privileged place on this planet. I wrote a book debunking that while at the same time pointing out that we are at a critical point in the evolution of life on earth, given our ability to modify the genetic code among others.

By dominant species, I'm referring to top predators in a given environment, not necessarily a single species ranging over the entire world at a given point in time.

Are there no species (or genus or order) that survive today from very early times? What about the horseshoe crab?

So it is quite acceptable to be disrespectful of creatures we are not descended from? I'll keep that in mind.

Where did I suggest that? I was referring to common perceptions. You're reading far more into my question than was ever intended or could be reasonably inferred.

I do have some good news for you. None of the rodent species alive today represent in any way the rodents from whom we evolved. So it's perfectly alright to swear at rats, fart in front of mice, and steal food from guinea pigs.

Please see the above reply.

 

[mgb_phys]

I think you are over-reacting slightly.
You have a good point that just because we are doing rather well in terms of top-predator and number of environments we thrive in today - some of our ancestors were hanging on by their little teeth.

That would be an interesting follow up to the Ancestor's tale. What else could have happened at each step, why didn't squirrels make it instead of monkeys, why didn't birds develop more intelligence than apes.

Anyway Bacteria rule the World, always have (since complex cells evolved) and always will - they are pretty much the only things that can do raw chemistry.

 

[jim mcnamara]

Ants are the dominant animal life form on Earth - per E O Wilson. He estimates they make up 30% of animal biomass. Green algae also probably won the evolutionary sweepstakes for plant biomass a long time ago.

As noted in the post above the big winner is bacteria. There are some papers on estimates of underground biomass, primarily archaebacteria. They posit there is as much biomass in the top few miles of crust, in the form of extremophiles, as there exists above ground.

So us humans still rank way down there...

 

[mgb_phys]

Ants are the dominant animal life form on Earth - per E O Wilson.

In spite of god's Inordinate Fondness for Beetles ?

 

[SW VandeCarr]

Ants are the dominant animal life form on Earth - per E O Wilson. He estimates they make up 30% of animal biomass. Green algae also probably won the evolutionary sweepstakes for plant biomass a long time ago.

As noted in the post above the big winner is bacteria. There are some papers on estimates of underground biomass, primarily archaebacteria. They posit there is as much biomass in the top few miles of crust, in the form of extremophiles, as there exists above ground.

So us humans still rank way down there...

That's why I defined dominant species in terms of being the top predator. I think I can argue that humans are the top predators in that we can eat (or otherwise destroy) virtually any individual living thing (including one of our own) in our environment. I think that's the way most biologists use the term. We know invasive species can completely displace indigenous species and in that sense become dominant even when not speaking in terms of predation.

EDIT: Can anyone speak to my original question: Are there any reasonably scientific descriptions of our ancestors at the major branch points along the human line of decent? (By major, I mean the branches off the human line of decent that lead to species that exist today.) Are there any such descriptions or better, drawings, in "The Ancestors Tale"?

 

[Ophiolite]

Are you going to deny the common perceptions? I never indicated I supported such perceptions. The common perception is that our species has a some privileged place on this planet. I wrote a book debunking that

I certainly deny those perceptions; I do not deny that they are commonly held. They also appear to be held by you. You state very clearly "We are the dominant species on the Earth today."
You state very clearly "It seems we are not descended from the most prestigious of lines."

I must accept that you do not actually hold those views, but I recommend you make your true views clearer so we can avoid pointless discussion in future.

By dominant species, I'm referring to top predators in a given environment, not necessarily a single species ranging over the entire world at a given point in time.

I'm sorry, but that simply makes no sense. You have said "We are the dominant species on the Earth today." That's one species ranging over the entire Earth. Now you are defining dominant species in a local environment. In the couple of acres around my house the dominant species is felis catus. Your statements are contradictory and ambiguous.

Are there no species (or genus or order) that survive today from very early times? What about the horseshoe crab?

No. None. Nada.
There is perhaps a genus or two, and certainly some families, however, your posts refer exclusively, up until now, to species. If you meant something else, why did you not say so?

Where did I suggest that? I was referring to common perceptions. You're reading far more into my question than was ever intended or could be reasonably inferred.

Wrong. You specifically stated that if we were descended from certain lines then we should be respectful of them. In English grammar, as in programming languages, such an if...then... construction very clearly implies if not ...then don't .
Again, I must accept that you did not mean this, but you sure as hell said it.

Can anyone speak to my original question:

Buy the Ancestor's Tale. You have had it recommended quite independently by two of us. It exactly addresses the question you have asked.

Are there any such descriptions or better, drawings, in "The Ancestors Tale"?

It is full of descriptions and even better, many references to the research on which it is based.

to Jim mcnamara and mgbphys, re the beetles, bacteria and ants, they are not the dominant species, since they contain very many species. I agree that one of these is in the running for dominant lifeform.

 

[cesiumfrog]

No. None. Nada.
There is perhaps a genus or two, and certainly some families, however, your posts refer exclusively, up until now, to species. If you meant something else, why did you not say so?

That question you quoted did contain the word genus, not exclusively species, but really I'm curious how (and in what sense) you can be so (triply) certain that no ancient "species" still survive? What about the triop, which has persisted hundreds of millions of years in temporary ponds by means of eggs (usually from cloning) that can remain dormant over very long periods? Or Wollemi pines? How exactly do you define "species" (to me this word sounds kind of unscientific)?

 

[SW VandeCarr]

Wrong. You specifically stated that if we were descended from certain lines then we should be respectful of them. In English grammar, as in programming languages, such an if...then... construction very clearly implies if not ...then don't .
Again, I must accept that you did not mean this, but you sure as hell said it.

Yes, I said that we must be respectful of these creatures which are held in particular popular contempt. This in no way implies that we shouldn't be respectful of all life. Note expressions like "You dirty rat." or even Shakespeare's "The Taming of the Shrew". Few people appreciate that we are the descendants of such animals.

Regarding the term "dominant species" in reference to humans, I gave a definition in previous posts. Is there any doubt we are the top predator? Given our technology, we hold the destiny of the planet in our hands. Yes, the planet will probably survive the worst we can do, but we are the engineers of a mass extinction that is happening now. Among the extinct will be Homo sapiens (perhaps not so sapient).

By the way, thank you for recommending "The Ancestor's Tail".

EDIT: Prior to humans I believe no known multicellular species had the range that humans have, so it makes sense to define a dominant species in terms of a local environment. Humans, however, effectively have access to the entire planetary surface.

 

[Ophiolite]

That question you quoted did contain the word genus, not exclusively species,

Correct, but the op only referred to species. If I were a cynical bastard I would suspect Sw of shifting the goalposts in order not to appear wrong.

but really I'm curious how (and in what sense) you can be so (triply) certain that no ancient "species" still survive?

This question is spot on. Any absolute statement should be challenged.

Firstly, I don't know of any species that are truly ancient. On the face of it that may look like the Argument from Ignorance fallacy. However, I have looked for examples before and have always been unsuccesful.

You introduced Triops (Triops cancriformis)as a possibility. I was unfamiliar with it. Certainly there are morphologically identical fossil examples of this reaching back to the Triassic, around 220 million years ago. I certainly concede that on the face of it - and using the palaeontological perspective I was trained in - this looks like a very long lived species. However, the palaeontological record fails to provide the insights available from good genetic analysis. Here are portions of a relevant abstract:

We investigated the phylogenetic relationships among the three presently recognized subspecies of the tadpole shrimp, Triops cancriformis, using mitochondrial 16S and 12S rDNA sequences. Our results indicate that the taxon is divided into two distinct lineages. One lineage is formed of T. c. cancriformis populations and samples from northern Spain that had been classified as T. c. simplex in the most recent literature. The second lineage comprises all populations of T. c. mauritanicus and northern African populations of T. c. simplex. These two main lineages separated 2.3 to 8.9 million years ago, based on the range of inferred molecular clocks recognized for crustacean mtDNA sequence divergence. Percentages of divergence are in the range reported for recognized species in other notostracan lineages and we therefore propose to recognize them as two species, Triops cancriformis and Triops mauritanicus.

Korn, M. et al "Sister species within the Triops cancriformis lineage (Crustacea, Notostraca)", Zoologica Scripta Volume 35 Issue 4, Pages 301 - 322 2006

Now if the genetic makeup of the beasts is sufficiently different after less than ten million years to justify seperating them into two different species, I think that is even more likely to be true over a span of time twenty times as great.

The same applies to the wollemi pine (Wollemia nobilis). To quote wikipedia, " The last known fossils of the genus date from approximately 2 million years ago", which is just yesterday geologically.

I have found exactly the same thing for every living fossil I have tried to track down: the family and sometimes the genus has been around for a long time, but never the species. Perhaps there is an exception out there - and my triple rejection of the idea may encourage someone to find it - but I rather doubt it.

Yes, I said that we must be respectful of these creatures which are held in particular popular contempt. This in no way implies that we shouldn't be respectful of all life.

Thank you for clarifying that. I've never paid much attention to popular thinking.

 

[SW VandeCarr]

Correct, but the op only referred to species. If I were a cynical bastard I would suspect Sw of shifting the goalposts in order not to appear wrong.

Biological classifications have shifted through the years and the difference between genus and species is not always that sharp. I've been told by a number of biologist that living members of the genus Limulus (horseshoe "crab", actually an arachnid) are nearly identical to members of the same genus from 270 to as early as 400 million years ago (within the limits that can be determined from fossil evidence). How precisely are we able to distinguish species within a genus based on 400 million year old fossils?

 

[WaveJumper]

The first mammal, 125 million years ago:

http://en.wikipedia.org/wiki/Eomaia
The first primate, 65 million years ago:

http://en.wikipedia.org/wiki/Purgatorius
Primate before the diversion of hominids and monkeys, 35 million years ago:

http://en.wikipedia.org/wiki/Aegyptopithecus

Transitional primate?, 17 million years ago:

http://en.wikipedia.org/wiki/Proconsulidae

This chart takes it up in more detail to the present day:

http://anthropology.si.edu/humanorigins/ha/a_tree.html
If anyone can add a missing link, please do.

 

[SW VandeCarr]

If anyone can add a missing link, please do.

Sorry, I can't supply the missing link (unless maybe it's me). I don't know why I couldn't find this in my searches. Many thanks WaveJumper. This is exactly what I was looking for. (Especially Purgatorius)

EDIT: I now find that Amniota are the common ancestors of both reptiles and mammals and that a species of reptile does not define a clade which includes humans. So apparently we can exclude reptiles from the human line of decent (but I still respect them).

 

[Ophiolite]

Biological classifications have shifted through the years and the difference between genus and species is not always that sharp. I've been told by a number of biologist that living members of the genus Limulus (horseshoe "crab", actually an arachnid) are nearly identical to members of the same genus from 270 to as early as 400 million years ago (within the limits that can be determined from fossil evidence). How precisely are we able to distinguish species within a genus based on 400 million year old fossils?

This branch of the discussion began with my statement that "The history of all species is that they do not survive."

A handful of genera apparently survive for a long time. However, this is based upon palaeontological data. These simply are, in most instances, not as rigorous, nor as revealing as the date and conclusions derived from genetic studies.

We cannot, in some cases, distinguish on the basis of hard part morphology between a genus alive today and one extant four hundred million years ago. What we can be confident of is that the genetic structure has changed significantly in that time.

 

[WaveJumper]

Sorry, I can't supply the missing link (unless maybe it's me). I don't know why I couldn't find this in my searches. Many thanks WaveJumper. This is exactly what I was looking for. (Especially Purgatorius)

EDIT: I now find that Amniota are the common ancestors of both reptiles and mammals and that a species of reptile does not define a clade which includes humans. So apparently we can exclude reptiles from the human line of decent (but I still respect them).

My pleasure. I'd spent a great deal of time researching this, glad it now helps other people too.